perf tools: Allow user to indicate path to objdump in command line

When analyzing perf data from hosts of other architecture than one of
the local host it's useful to call objdump that is part of a toolchain
for that architecture. Instead of calling regular objdump, call one that
user specified in command line.

Signed-off-by: Maciek Borzecki <maciek.borzecki@gmail.com>
Acked-by: David Ahern <dsahern@gmail.com>
Link: http://lkml.kernel.org/r/1346754750.16299.3.camel@localhost.localdomain
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>